From the moment Dev was aware of his mother's past he was lost and completely relied on Sonakshi for strength and direction. When Sona made possible the impossible, relieving Ishwari of her burden by bringing Khathri's truth out and a chance for atonement of her mistake, Dev saw his mother embracing her without inhibition. It was something he had wished for with all his heart. But Ishwari and maami's conversation made him realize that even though his mother embraced Sonakshi the girl who went out of her way to heal them, she still had reservations regarding her ex-DIL. Sonakshi's words before their separation on how he failed to bind them with love might have been ringing in his ears when he left from there.
Along with the realization on how difficult it was for his mother to accept Sona wrt their past it also made him understand that it must have been difficult for Sona to do what she did for them. She knew that if her leaving him broke him, it would kill him if something happens to his mother. So whatever she did was for him. This recognition was playing in his mind when Sona interrupted his thoughts, asking him to share his problems with his" friend". Mr. Perceptive Dixit saw that his "khargosh" was trying to hide her love as the concern of a very dear friend. So of course he asked whether she does this for all her friends and knew that her hands were tied just like his were before. He understood both the women in his life like the palm of his hand but they failed to understand each other and it was his failure. Once he realized it he set about to right the wrong.
It was so endearing to see their excitement knowing that both the families are putting in a conscious effort to break the barriers to be at least cordial with each other. Seeing Sona seated with her family in his home with all due respect and his mother trying her best to be the perfect host and welcoming them with all her heart made Dev so jubilant that he was glowing with happiness. He was drinking in that sight like a man dying of thirst. Sona kept looking at him, his happiness and excitement perfectly in sync with her. Their family sitting together amicably without being at each other's throat was something they never thought might happen in this life time and their happiness knew no bounds which they shared with each other, their eyes doing all the talking. The time stood still for them.
When Sona went to the kitchen to help Ishwari they interacted with the same kind of warmth they had for each other when Sona was just her doctorni, until Dev came. They both felt awkward while Dev cruised along as if it was perfectly natural. But his effort didn't go un-noticed.
Because it was both their heart's deepest desire Sona knew instinctively that Dev made this happen. They stood together admiring their family getting on with each other from afar, Dev calling her khargosh and Sona responding to his endearment because they were finally in that happy place. Dev doesn't want to push Sona and also know that she is not ready to give more than what she is giving now even though she still loves him deeply. She is bound by the promise she gave to her father and unless and until Bijoy feels that Sona will be taken care of like he expects her to be and relaxes his stance she will be incapacitated by it. Dev is in a place now where he can understand Bijoy's fears and his irrational behavior. Time was something they were deprived of and he was willing to give just that to their relationship to let it blossom again with the blessings of their family.
Sona showed her vulnerable side when she called Dev after he left her to deal with the power cut. But once he understood that she needs him he never once left her side even when they were unable to locate Soha and Golu's whereabouts only making sure that his mother will be fine asking her to stay wherever she was.
Elena and Vicki had been side heroes all their life to Sona and Dev which was what brought them closer. Vicki used the same reference knowing fully well how much it will hurt her. He had always hated the comparison and this hatred is his driving force which he wanted Elena to take too. It is so sad that he doesn't even know how wrong he is. If by any chance he does win his goal he will lose Golu forever. Golu will hate him just the way he hated Dev all his life.